1. Field of the Invention
The present invention is directed to an automatic x-ray exposure unit, and in particular to an exposure unit suitable for use in mammography.
2. Description of the Prior Art
In x-ray technology, for example in mammography, a detector for the automatic exposure unit is generally arranged behind the film-foil system. In conventional automatic x-ray exposure units, this results in the exposure to which the examination subject is subjected being dependent on the subject thickness. An automatic transparency matching is possible if, as disclosed in German OS 30 08 261, a detector having two detector elements is used, with the radiation incident on each detector element being differently filtered, and the quotient of the signals from the detector elements is formed. This quotient is thus a transparency-dependent signal, which can be used for balancing the automatic exposure unit.
Despite the automatic transparency matching, an optimal exposure only results in this known system when the position of the measuring field can be brought into coincidence with the densest region of the mammory gland.